7-day in Croatia

Aside from Googling (including "fall" or "winter" in the queries), you might see whether the Croatian tourist office has any advice. I assume that public bus service to Plitvice Lakes is cut back (if not eliminated) at that time of year, and I think one-day bus tours are unlikely that late in the season. I believe the Zagreb-Split-Dubrovnik public buses will be running at a decent frequency, but that's just a guess. Zagreb to Split is also possible by train.

Seven days is a rather short time to squeeze in all 4 of your destinations. I'd definitely drop Plitvice (even if it's accessible) if the weather is poor. I was in Zagreb the second week of October 2015, and the weather changed from summer to fall, turning very cool and wet. I assume the temperature will be more moderate along the coast than in Zagreb for your timeframe. But Zagreb is a lively city with good museums to visit and rather short distances to walk. I'd consider it a decent destination in November/December (though I, personally, would never go to Europe that late in the year).

Zadar would be a good stopover on the way from Zagreb to Split.

The busses should still be running between the major cities (Zagreb -> Split -> Dubrovnik) and that's going to be your best way to get around. Because you are limited on time, you should consider flying on Croatian Air between Dubrovnik and Zagreb. This allows you to do a one-way trip rather than double-back on yourself.

Although it was in May, my wife and I came into Zagreb on the train from Hungary. The next day, we had a private tour guide take us to Plitvice Lakes, take us around the lakes, and then back to Zagreb. That way, we were not beholden to the bus schedule and got to chat quite a bit with the guide. The following day, we flew to Dubrovnik and then worked our way up the coast to Split, and then back to Zagreb where we caught our flight to Paris. You may want to try something similar given your constraints.

Hope this helps!